IL-6 is a cytokine generically referred to as B cell stimulating factor 2 or Interferon .beta.2. IL-6 was discovered to be a differentiation factor involved in activation of B lymphocytic cells (Hirano, T. et al., Nature 324, 73-76, 1986). Later, it was shown to have an effect on the functions of various cells (Akira, S. et al., Adv. in Immunology 54, 1-78, 1993).
IL-6 is a multi-functional cytokine that acts at various stages of immunity, hematopoiesis, acute phase reactions and so forth (Taga, T. et al., Critical Reviews in Immunol. 1992; 11: 265-280), and in addition to acting as a growth factor of multiple myeloma, has also been reported to be involved in various diseases such as illneses in which plasmacytosis is observed including rheumatism (Hirano, T. et al., Eur. J. Immunol. 1986; 18: 1797-1801; Houssiau, F. A. et al., Arth. Rheum. 1988; 31: 784-788) and Castleman's disease (Yoshizaki, K. et al., Blood 1989; 74: 1360-1367; Brant, S. J. et. al., Clin. Invest. 1990; 86: 592-599), or mesangial cell proliferative nephritis (Ohta, K. et al., Clin. Nephrol. (Germany) 1992; 38 185-189; Fukatsu, A. et al., Lab. Invest. 1991; 65: 61-66; Horii, Y. et al., J. Immunol. 1989; 143: 3949-3955) and cachexia accompanying tumor growth (Strassman, G. et al., J. Clin. Invest. 1992; 89: 1681-1684).
In H-2Ld hIL-6 transgenic mice (IL-6 Tgm), in which human IL-6 (hIL-6) was expressed in excess by genetic engineering, IgG1 plasmacytosis, mesangium proliferative nephritis, anemia, thrombocytopenia and the appearance of autoantibodies were observed (Miyai, T. et al., 21st Japan Immunol. Soc. Pres. "Hematological and Serological Changes Accompanying Aging in H-2Ld hIL-6 Transgenic Mice": 1991), thereby suggesting that IL-6 is involved in various diseases.
In addition, IL-6 is also known to have the effect of promoting muscle protein proteolysis in myoblasts in vitro (Ebisui, T. et al., Clinical Science, 1995; 89: 431-439).
However, it has heretofore been unknown that antibody to interleukin-6 receptor is effective in inhibiting proteolysis of muscle proteins, and such attempts have yet to be made.